Desirable features of a heat generating system, particularly one which is used to heat a structure, include reasonable:
1. control over thermal output, PA1 2. means to transfer thermal output to the environment to be heated, PA1 3. operational safety, PA1 4. operational efficiency, and PA1 5. operational convenience.
Solid fuel burning stoves as thermal generating devices have been deficient in most, if not all, of the above features because it is very difficult to control the combustion rate of their fuel. This is due to the fact that, once ignited, most solid fuel fires, when provided with sufficient oxygen, tend to be self-propagating. The more the fuel burns, the more it tends to create conditions favorable to more intense burning, limited only by the availability of fuel or oxygen. Control of the combustion process can be established by limiting the supply of oxygen to the fire; however, to maintain the stove's temperature within a range of approximately 200 degrees Fahrenheit to 400 degrees Fahrenheit necessary for safe and efficient operation, the operator must constantly monitor the stove's performance and make adjustments of the air intake accordingly.
If flue gas temperatures are allowed to fall below 200.degree. F. when wood is used as a fuel, creosote which is a flammable byproduct of low temperature combustion begins to accumulate on the inner surface of the flue and chimney, creating a potential fire hazard. If temperatures are allowed to exceed 400.degree. F., potentially useful heat is wastefully vented into the atmosphere in large quantities and the exhaust components of the stove may overheat to produce a potential fire hazard.
Other problems with solid fuel burning stoves are regulating the thermal output within the optimal temperature range to meet specific heat demands and the transfer of heat to desired locations. Again these can be controlled if the operator is willing to constantly monitor the performance of the stove and ambient air temperature of the structure, and make adjustments accordingly. Monitoring of the stove and the environment temperatures on the continuous basis required for the safe and efficient operation of the system is obviously not a practical alternative for most solid fuel stove users.